There has been a long sought need for a reliable detection procedure which would verify the identity of precious stones such as diamonds. Conventional methods of identifying diamonds relied upon photographs and/or written descriptions of the physical fearures of the stone such as the shape, cut, weight, measurements, proportions and the like. It was difficult using these variables to locate and recover specific pieces of lost or stolen jewelry especially if the items were altered as by cutting, drilling or polishing.
A protection system which would provide a dependable method of recognition would thus be particularly useful not only to jewelry owners but also to the insurance industry.
A prior scheme for identifying diamonds involved the process of photographing a pattern of reflections created when a low level laser light beam was passed through the stone. This reflection pattern was then stored in a computer at a central registry for later use. A disadvantage of this system was that by altering the diamond surface structure such as by repolishing a facet, the reflection pattern could be changed thus defeating the possibility of subsequent reidentification.
Another shortcoming of that system was that local jewelers had to acquire the laser and photographic equipment for making the photographs, and furthermore later identification was dependent upon verification from the central registry.
The ability to inscribe permanent markings directly in a diamond could have expedited the identification procedure and furthermore could also have served as a theft deterrent.
A problem encountered in the prior art with regard to inscribing on diamonds was to develop an effective method for penetrating the extremely hard surface without damaging the diamond. Although the use of laser energy was previously applied for altering the surface of a workpiece such as typically illustrated in U.S. Pat. Nos. 4,336,439 and 4,028,532, those procedures were not directed to engraving in a diamond surface and consequently were not concerned with the problems inherent when inscribing in this material. Other attempts at laser inscribing were noted in U.S. Pat. Nos. 3,657,510 and 4,032,861. These last mentioned methods utilized a mask having a cutout portion defining a given pattern and did not contemplate engraving in a diamond surface in characters that were invisible to the naked eye. Another method for working diamonds with the use of laser energy was shown in U.S. Pat. No. 3,537,198. That method, however, did not solve the problem of controlling the depth of laser penetration and engraved line size.
By way of further background, it should be understood that in order for the electromagnetic laser radiation to vaporize the diamond surface, a critical energy level must be reached. Radiation below this threshold energy level is transmitted through the diamond. When the laser power supply source is increased to produce laser energy above the critical level, the diamond surface will vaporize forming carbon and pyrolithic graphite which, in turn, absorbs further energy in an uncontrolled avalanche effect producing a deep penetration mark. That procedure was unacceptable when working with diamonds which require precise control over depth of cut or subsurface marking.